By Brendan Smith and Jeremy Brecher

Not worried about climate change? How about the health of you and your family?

For decades the public health community has been trying to get us to understand that climate change affects the fundamental requirements for health ““ clean air, safe drinking water, sufficient food and secure shelter. Their research reveals this is not some distant threat — it’s here and now and already responsible fore more than 150,000 deaths and 5 million illnesses every year.

And with climate-linked disease tolls expected to double by as soon as 2030, the crisis is only going to get worse.  Our doctors are sounding the alarm that climate change poses the biggest threat to human health in the 21st century, and before it’s too late, we need to heed their warnings.

Here are six reasons why the public health community is so worried:

Fatal Diseases are Becoming More Virulent and are Spreading: Many of the most deadly diseases on earth — malaria, dengue and yellow fever, encephalitis and cholera — are highly climate sensitive, and as a result, are spreading to new parts of the globe — including the U.S. Dengue fever, for example, has rarely been seen in the U.S. but is now appearing in Florida. An additional two billion people will likely be exposed to this deadly virus over the next 60 years. Rodents, insects and other disease host populations are exploding. Parasites and microbes are marching steadily northward, with infections such as Lyme disease increasing tenfold in the past 10 years.

Rising Death Tolls Caused by Extreme Weather Events: Globally, the number of reported weather-related natural disasters — ranging from floods and hurricanes to heat waves and tsunamis — has more than tripled since the 1960s, taking the lives of more than 60,000 people a year. These numbers keep going up. The 2003 heat wave in Europe killed more than 70,000 people; nearly 2,000 died from the 2010 flooding in Pakistan; and here at home, the 2006 heat wave killed 450 people and sent 16,000 to the emergency room. Researchers expect that these extreme heat waves will be commonplace by 2039. And lest we forget, 1,836 people died in Hurricane Katrina. In California alone, researchers predict up to four times as many heat-related deaths in San Francisco, Los Angeles, San Bernardino, Sacramento, and Fresno, including 600 or more extra heat-related deaths per year in Los Angeles County.

Rising Rates of Asthma and Other Respiratory Diseases: Increasing temperatures are raising the levels of ozone and other pollutants in the air as well as driving up pollen and other aeroallergens. According to Dr. Cecil Wilson, president of the American Medical Association, climate change has “extended the allergy and asthma season, in this country, by about 20 days. Asthma rates have doubled and other respiratory diseases are also on the rise.” Urban air pollution already claims the lives of 70,000 Americans a year, the same number that die from breast and prostate cancer combined. A recent study in the Proceedings of the National Academy of Sciences drew a direct connection between hotter weather and a longer pollen season — which impacts the lives of more than 36 million Americans who suffer from seasonal allergies.

Diminishing Quantity and Quality of Fresh Water Supplies: Climate change is rapidly shifting rainfall patterns, causing more sever and frequent droughts and flooding. Scientists predict a permanent drought by 2050 throughout the Southwest US. By the 2090s, climate change is likely to double the frequency of extreme droughts and increase their average duration six-fold. From a public health perspective, droughts compromise hygiene, increase the risk of diarrhoeal disease, and trigger famines; while flooding contaminates freshwater supplies and heightens the risk of water-borne diseases.

Spread of Food-Born Illness: Besides triggering food shortages and driving up food prices, climate change is also spurring the spread of food-born bacteria and other diseases. Researchers at Michigan State University traced a 2006 salmonella outbreak in the US to lettuce grown in Spain and shipped to Finland. The cause was linked to farmers using untreated water for irrigation, who were forced to use contaminate water because a drought — likely triggered by climate change — had restricted their access to clean water. And NOAA scientists recently warned that rising ocean temperatures will lead to more toxic algae blooms and proliferation of harmful microbes and bacteria, all of which will contaminate shellfish and other seafood.

Disappearance of Nature’s “Medicine Cabinet”: Over 50% of all prescription medicines are based on chemicals from plants and animals. But just as diseases are becoming more virulent and are spreading, climate change is also threatening to wipe out “nature’s medicine cabinet” — a resource humans have relied on to protect themselves for hundreds of years. According to a study published in Nature, up to 37% of known plant and animal species will be “committed to extinction” by 2050. One example that is already raising alarms is the rapid decline of horseshoe crabs — which we rely on to ensure injections are free of bacterial contamination.